The reliable functioning of optical components is of critical importance in optical systems, which typically have small tolerances. Parameters such as device efficiency (which describes the amount of conversion between electrical and optical energy) govern the performance of an optical system. For example, optical systems which utilize semiconductor lasers as light sources can lose performance due to heating of the laser at high power levels and the consequent well-known phenomenon of efficiency rollover.
Prior art methods for the characterization of optical devices have relied upon measurements made by calibrated optical detectors, which produce a signal proportional to the incident light power. See, for example, U.S. Pat. Nos. 5,678,924 and 5,743,641. These methods can be hampered in situations where such detectors are not available (as is true for certain wavelengths of light) or are not able to be positioned in the path of the light. The latter can be the case in integrated photonic systems in which optical elements emit light laterally into immediately adjacent fabricated components. Additional complications with calibration arise when optical systems employ devices at many different wavelengths.
The use of a thermal sensor in the control of laser power has been previously proposed in U.S. Pat. No. 6,101,200. However, this prior method relies upon an optical detector to determine the desired amount of optical power; device temperature is then probed at this bias point and a thermal sensor is later used in conjunction with a thermoelectric cooler merely for feedback control. Since this prior method relies on an optical detector, this prior method is inapplicable in the case of integrated photonic systems, and also is not appropriate for the determination of device parameters over a range of bias.
In view of the foregoing it would be desirable to provide a method and apparatus for characterizing devices and circuits. It would be further desirable to provide such a method and apparatus using a thermal sensor to measure optical device and circuit parameters.